ELI5: Explain Like I'm 5

Fusion tree

Imagine you have a big box full of apples, and you want to find a particular apple named "Sally". To do this, you might start by looking at one half of the box, and if you don't find Sally there, you could then look at the other half. This is like the way a binary search works.

But suppose you have millions of apples in your box. Doing a binary search each time you want to find an apple would be very slow. So, you might want to use a more efficient approach. This is where a fusion tree comes in.

A fusion tree is like a special kind of organizational system for your apples that helps you find them more quickly. Instead of just dividing your box in two each time, you can divide it into two smaller boxes, and keep doing this until you have many small boxes each containing just a few apples. Each of these small boxes is called a "node".

Think of the fusion tree as a special kind of map that shows you which apples are in which nodes. So, if you want to find Sally, you would start by looking at the top node, which contains all the other nodes in the tree. From there, you can follow the map to find the node that contains Sally, and then find her within that node.

The great thing about a fusion tree is that it's very efficient at finding things, even when you have millions of them. It's like having a superpower that lets you find anything you need in an instant, even if it's buried deep within a huge pile of stuff.

In summary, a fusion tree is a special kind of organizational system that helps you find things more quickly and efficiently by dividing a large group of items into many smaller groups called nodes, each with just a few items. It's like a superpowered map that lets you find things instantly, even if you have millions of them.